Trim circuits used in high reliability applications such as satellites must be able to perform reliably over the entire life of the satellite. For a trim circuit this means that the trim circuit reliably holds the state to which it was originally programmed. Traditional trim circuit techniques using one time programmable fuses made of polysilicon or metal are known to be sensitive to regrowth over time when a bias or electrical potential is constantly applied across the terminals of the fuse. If the fuse cell is not properly designed, regrowth in the fuse cell can result in changes to the state for which it was programmed, which can result in erroneous performance of the circuit in response to the trim code or even catastrophic failure.
The issue of fuse regrowth is typically overcome by employing a latch on power up to hold the value of the fuse cell and removing any bias from the fuse to mitigate regrowth. However, space electronics must survive exposure to high-energy protons, electrons, and, occasionally, heavier ions. These energetic particles can temporarily change the state of the latched cell and under the right circumstances can cause permanent change to the latch, again resulting in unintended circuit behavior and/or permanent failure. Keeping a circuit free of the results of high-energy encounters can require triple-redundant latches that are periodically compared with each other and corrected when one latch has a different value from two corresponding latches. These additions add greatly to the size and complexity of the circuitry.